A welding robot is now being widely used for performing arc welding with a welding torch for arc welding that is attached to the tip of a vertical articulated robot.
FIG. 5 shows the outward appearance of this welding robot. In FIG. 5, reference numeral 51 denotes a vertical articulated robot; and reference numeral 52 denotes its upper arm. A wrist 53 which can perform the operation with three degrees of freedom (slewing, swing and rotation) is attached to the tip of the upper arm 52. Reference numeral 61 denotes a wire feeding device. The wire feeding device 61 is fixed to the upper arm 52 to extract a welding wire 63 from a wire reel 62 and extrude the welding wire 63 to a welding torch 64 attached to the wrist 53. Reference numeral 65 denotes a welding cable. The welding cable 65 connects the wire feeding device 61 and the welding torch 64. The welding cable 65 is provided with a tubular passage at the center through which a welding wire is passed. The welding cable 65 binds a hose for supplying a sealed gas, an electric wire for supplying a welding current and various kinds of signal lines, which are arranged around the tubular passage.
Meanwhile, in such a conventional welding robot, the wire feeding device 61 is fixed to the upper arm 52. The welding torch 64 attached to the wrist 53, which performs the operation with three degrees of freedom, moves freely. The welding cable 65, therefore, repeats bending or twisting. This presented a problem that the welding cable 65 might be broken owing to stress.
Particularly, if the welding cable 65 is located near the upper arm 52 and wrist 53 (as shown by dotted line in FIG. 5) in order that it does not interferes with objects in the vicinity of the robot 51 (e.g. a welding workpiece or jig), the bending radius is small and the length is also short. The bending stress and twisting stress, correspondingly, become large. This presented a problem of further shortening the life of the welding cable 65.